U.S. Sen. Mark Udall leads Republican challenger Cory Gardner by 4 percentage points in a new Denver Post poll that shows the Democratic incumbent is ahead among unaffiliated and female voters.

The poll showed Coloradans are split over which candidate would make the best decisions in office and who is more trustworthy.

The race “could go either way” at this point, according to SurveyUSA, which conducted the poll this week for The Post. The poll has a margin of error of plus or minus 3.9 percentage points.

Udall received 46 percent support to Gardner’s 42 percent in their high-stakes, high-dollar race that could determine which party controls the U.S. Senate after the Nov. 4 election.

“It is a very tough year to be a Democrat,” especially at the federal level, said Eric Sondermann, a Denver-based independent political analyst. “(Udall) would much rather be four points up than four points down. But he’s still in a difficult race and a difficult climate.”

Udall, who has hammered Gardner on social issues, including abortion and birth control, has a 13-point lead among women. Gardner, a two-term congressman, is making inroads in a crucial voting block, with Colorado Hispanics, giving Udall only a 2-point lead.

The poll shows Udall leading by 19 points in the populous Denver area — where Jefferson and Arapahoe counties are considered crucial in determining the winner. Gardner leads everywhere else, including by 11 points in greater Colorado Springs and by 16 points in the rest of Colorado.

Among those outlying Gardner supporters: 71-year-old Ken Rinker, a Craig Republican who was called by SurveyUSA on Wednesday night.

“Mark Udall is basically trying to destroy the economy in this part of the state by shutting down coal mines and closing coal-fired power plants,” he said.

“I know Udall supported Obamacare, which I’m against, but part of it is I think he’s running a more positive campaign,” she said. “He seems to be more grounded and more real.”

The sample of voters polled was evenly divided among Republicans, Democrats and unaffiliated voters at 33 percent each. Owen Loftus, spokesman for the Colorado Republican Party, pointed out 2014 is expected to be a GOP wave year.

“Only in the most wild fantasies of the Bannock Street Boys will there be as many Democrats voting in 2014 as there are Republicans,” he said, referring to the Democrats’ victory effort.

Jay Leve, president of SurveyUSA, said had the poll reflected actual statewide voter registrations, where Republicans have more members than Democrats (unaffiliated voters are the largest group), the results still would show Udall in the lead.

The Senate poll shows that only 7 percent of Coloradans are undecided, while unaffiliated candidate Steve Shoganreceived 3 percent of the vote and Libertarian Gaylon Kent got 2 percent.

Udall received higher unfavorable marks than Gardner at 47 percent, with 40 percent favorable, while 13 percent of Coloradans said they need to know more about the first-term senator.

Voters were tied at 36 percentage points when asked whether they had a favorable or unfavorable opinion of Gardner, with 28 percent saying they need to know more.

The Denver Post’s poll by SurveyUSA was conducted Sept. 8 through Sept. 10 of 850 Colorado adults and narrowed to 664 likely voters. SurveyUSA contacted both land lines and cell phones.

The poll results have a margin of error of plus or minus 3.9 percentage points. Pollsters weighted the sample by gender, age, race and region, but not by party identification. The party affiliation breakdown of the sample, with numbers rounded, was 33 percent Republican, 33 percent Democratic and 33 percent unaffiliated.

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